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Islatravir PrEP Implant Could Prevent HIV for a Year


Jim Allen:
Pretty cool results. Looking forward to seeing more development on this one as once a year implant would be very cool.

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--- Quote ---Islatravir PrEP Implant Could Prevent HIV for a Year
A next-generation implant maintained adequate drug levels for at least a year in an early study.

An experimental islatravir implant that can be replaced just once a year could one day be a convenient new option for HIV pre-exposure prophylaxis (PrEP), according to early study results presented this week at the virtual Conference on Retroviruses and Opportunistic Infections (CROI).

Formerly known as MK-8591, islatravir is a first-in-class nucleoside reverse transcriptase translocation inhibitor with multiple mechanisms of action. It has a long half-life in the body, suggesting it has the potential to be taken once weekly for HIV treatment or once monthly—or less—for PrEP.

At the 2019 International AIDS Society Conference on HIV Science, Matthews presented the first data from a Phase I clinical trial of a prototype islatravir implant, showing that drug levels remained above the threshold found to be protective in monkeys for at least 12 months.

At CROI, Matthews presented results from a follow-up study of an updated version of the implant. While the older implant contained only islatravir and a polymer that releases small amounts of the drug over time, the next-generation version is easier to manufacture and includes a barium tracer that makes it visible on an X-ray, in case it migrates away from the insertion site. The implant, about the size of a matchstick, is administered using the same applicator as the widely used Nexplanon contraceptive implant.

This study included 36 men and women at low risk for HIV. Twenty-four of them received implants containing 48, 52 or 56 milligrams of islatravir, which were inserted under the skin of the upper arm and left in place for 12 weeks. For each dose level, eight people received islatravir implants and four received matching placebo implants. They were followed for an additional eight weeks after the implants were removed.

Regardless of dose, levels of islatravir triphosphate (the active form of the drug) reached and remained above the target effective threshold for 12 weeks and then began to decline. The highest-dose implant produced protective drug levels for about 16 weeks—four weeks after removal of the implant—while the lower doses fell below the threshold sooner. The researchers projected that the 56-mg implant should release adequate levels of islatravir for almost all individuals for more than 52 weeks. This will offer some forgiveness if replacement is delayed, Matthews said.
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